Large carnivorous water bear
Milnesium tardigradum
ORDER
Apochela
FAMILY
Milnesiidae
TAXONOMY
Milnesium tardigradum Doyére, 1840, close to Paris, France.
OTHER COMMON NAMES
None known.
PHYSICAL CHARACTERISTICS
Measure 0.0197–0.0236 in (500–600 µm), females sometimes up to 0.0394 in (1,000 µm), males much smaller. Body is elongated to torpedo shaped; color varies from colorless to reddish or brownish and black eyes are posterior on each side of the pear-shaped pharynx; head region displays a number of unique characteristics. Terminal mouth opening is surrounded by six robust, triangular lamellae that serve as closing apparatus for mouth opening when it is not feeding; has six oral and two lateral papillae, which may have chemoreceptory function. Double claws unusual because primary and the secondary branches are completely separate; primary branch is very long and flexible, while secondary branch is a short and robust claw, usually with three spurs. Buccal tube is wide and short, and armed with short convex stylets and stylet supports.
DISTRIBUTION
Commonly cosmopolitan; from dry tropical deserts to polar freshwaters; M. tardigradum is actually a complex of several species; is also one of the tardigrade species that are present in the fossil records. A eutardigrade found in Cretaceous amber from United States, described as M. swolenskyi, is very similar to M. tardigradum, meaning they probably lived together with the dinosaurs. (Specific distribution map not available.)
HABITAT
Particularly common in drier temperate terrestrial habitats such as mosses and lichens; one of the first described species from mosses on roofs and in gutters of houses; species recorded from supralitoral lichens of the genus Ramalina and from ornitho-coprophilous lichens (grow in bird feces) such as the yellow Xanthoria elegans. In these lichens, it is colored reddish to brownish.
BEHAVIOR
A fast "runner," moving in a very characteristic way, and does not use its fourth pair of legs. Almost stands up, like a mini carnivore dinosaur, when it attacks prey.
FEEDING ECOLOGY AND DIET
Exclusively carnivorous, feeding on nematodes, rotifers, and other smaller eutardigrades. Large nematodes are attacked at the middle of their trunks and pierced by the two stylets; cell contents of nematode are sucked out by strongly muscular pharynx. Smaller nematodes swallowed like spaghetti. The mid-gut can be filled with jaws from rotifers; genus Philodina may be a favorite diet. Bucco-pharyngeal apparatus of smaller tardigrades also found in the mid-gut of the species.
REPRODUCTIVE BIOLOGY
Fertilization is internal; female has a single seminal vesicle, which has been mistaken for a fourth malpighian tubule. Males are much smaller than females; male claws on the first pair of legs are strongly modified; secondary branch of the double claw is a rough and robust hook; assumed that males use claws to attach to female during mating; up to 18 smooth-shelled eggs deposited in the cast exuvium. The size of the eggs ranges from 0.00276 to 0.00453 in (70–115 µm). Newly hatched juveniles resemble miniature adults.
CONSERVATION STATUS
Not listed by the IUCN.
SIGNIFICANCE TO HUMANS
Has been used for pest control of nematodes in soil, but without very good results.
